Anti-biofouling copper-base alloy



United States Pater 2,887,374 ANTI-BIOFOULING COPPER-BASE ALLOY Carl L. Bulow, Trumbull, Conn., assignor to Bridgeport Brass Company, Bridgeport, Conn., acorporafion of Connecticut N 0 Drawing. Application May 25, 1955 Serial No; 511,107

This invention relates generally to copper-base alloys and more particularly to a brass lalloy having superior characteristics'with"respect to biofouling andcorrosion effects.

Copper and zinc melted together in variouspropon tions produce one ofthe most useful groups of alloys,

designated as the brasses. Other elements present in the copper-zinc system of alloys are either impurities which were not removed during processing or are those intentionally added for specific purposes. Thustin is frequently added to copper-zinc systems in varying concentrations to improve its corrosionresistance and to increase its strength and hardness.

Brass alloys are widely-used for the construction of apparatussubjected to corrosivesolutions. For example, in the manufacture of condenser and heat exchangetubes, marine 'hardware'and shafts, ferrules, valves andother elements which come in contact with sea water, it is conventional to make use of copper-zinc alloys such it as Muntzmetal, Admiralty metal or aluminum brass.- Brass is also employed for fresh water supply lines and tanks,

as well as in industrial andchemical plant equipmentinvolving exposure to a wide variety of acid and saline solutions.

Copper-base alloys are susceptible to various typesof corrosion which gradually weaken the alloy and ulti-- times in isolated areas? where" the dezincification is ill? tensified, thereby pitting: and eventually penetrating the tube wall to produce a leak therein. This intensified form:

ofcorrosion isdusu'ally referredtoasfplug type" dezincification. The, attack on metal by flowing water is further augmented by the turbulence of the liquid; resulting insocalled impingement-corrosion.

' Conditionsconducivewto stress corrosion failure, or as it is more commonly called, season cracking, arethe lowed: by exposure to ammonia or ammoniacal com pounds. Such exposure occurs where thesbrass tube is in contact with natural waters (fresh or salt), whereby an algal film or slime is gradually formed on the surface of the metal: The formation of an organic slime on metal is generally designated biofouling. As is well known, algaehas a high protein coutentjand upon decomposition thereof ammonia products are released. Hence,.a brass tube in natural water issubjecttto, corrosi on duer to biofouling as well as the usual corrosion effect resulting from the chemical action of a saline or mineral solution and brass: ,Ana extensive discussion of the-corrosive eflect of marine flora and fauna on copperbisealloys may be found in the"article of ,C. L. Bulow,

entitled Corrosion and Biofouling of, Copper-Base Al: loys in .Sea Water, appearing in the Transactions of the Electrochemical Society, volume 87, 1945, pages3l9 to, 352. In this article, the test results are given for a total of 240 test pieces of copper alloys of widely varied com-- position. These pieces are exposed to clean, flowing sea. water for periods of six to twelve months, during which the water temperature ranges between 2 and 30 C. All of the specimens were coveredwith. slime after a few months exposure.

While it is known to add a small amount of arsenic. to'a copper alloy to reduce dezincification effect, the addition of arsenic does not materially-inhibit the forma: Indeed, in,

tion of algae on the surface of. the metal. some instances, arsenic has been found to have the reverse efiect and appears to attract certain forms of marine organisms. I

The formation of algae or bacterial ,slimes on thesurface of a brass tube not only contributes toward corro-' sion but also impairs the heat transfer properties of the tube. A slime formationon the wall of a tube acts as a heat insulator, hencewhere the tube is incorporated in a heat exchanger, this factormaterially lowers the efficiency of the system. Heretofore, it has been necessary to chlorinate the system to retard or prevent the formation of algae.

Accordingly, it is the principal object of the invention to produce a copper-base alloywhichhas superior resistance to corrosion and biofouling effects.

More particularly, it is, an object of the invention to provide a brass alloyincluding analgae inhibiting agent.

Still another object of the invention is to provide a brass alloy characterized by a reduction in the tendency toward dezincification, a reduction in the rate of impingement attack as well as a reduction in the amount of of approximately 60 to zinc, in the range of ap-" proximately 15 to 40% andmercury-inthe range of approximately .001 to r 1 Due to the volatility of mercury, it cannot be, directly;

introduced into, the molten-brass since the mercury will quickly vaporize and be driven off. Accordingly, the preferred technique for forming a copper-zinc-mercury alloy is by the process of amalgamation. An amalgam is first-produced by treatment of copper or zinc with a solution of mercury salt under conditions such as to precipitate metallic mercury on the surface of the metal. This is accomplished, for example, by soaking small paricles or chips of zinc or copper in a mercurous nitrate solution having a small amount ofnitric acid added" thereto, whereby metallic mercury is precipitated on the surface of the chips by electrolytic exchange. No electrical current is required for this purpose.

The mercury so deposited'forms'a superficial amalgam on the surface of the chips. The mercury-plated chips are washed and dried and thereafter are introduced to; the molten base metal to form the desired alloy. The ratio of mercury to copper and zinc may be controlled by the relative amount of chips introduced into the molten metal. Alternatively; the alloy maybe formed by the use of zinc, copper, or copper alloy containingqa small amount of mercury asa natural impurity or alloying element. e l

It has been found 'that' the additionof mercury to copper-base alloys produces a substantial improvement in general corrosion resistance and impingement corrosion towards seawater as well as improved 1 resistance Moretowards dezincification. The inclusion of mercury in brass compositions has been found to have very significantly reduced the extent of biofouling by various marine organisms. Even such alloys as high brass and Admiralty, which are generally subject to biofouling by algae and bacterial slimes, remain very clean and brassyb right when incorporating mercury. Residual slime clinging to the surfaces adheres poorly thereto and can be much more readily rinsed from the surface when the alloy includes mercury as disclosed herein.

In Table 1, examples are disclosed of alloys in accordance with the invention, the main constituent of the alloys being set forth in percentage values. In order to provide a basis for comparison of the characteristics of the alloys in accordance with the invention with similar alloys in which mercury is absent, Table 1 also includes under each example a conventional mercury-free alloy whose constituents otherwise have about the same relative percentages. Examples D, E, F, G and H are closely related with respect to the relative proportions of copper and zinc, hence these examples are compared with but one similar mercury-free alloy.

Table 1 (In percentages) Example A Cu. 65.03-Zn 34.95-Hg .04 High brass Cu. 65.92-Zn 34.8l-Hg .00

Example B Cu 60.16-Zn 39.83-Hg .07 Muntz metal... Cu 59.75-Zn 40. 23-Hg .00

C11 71.14-Zn 27.84-Su .96-Hg .05 C11 71.10-Zn 27.98Sl1 .97-Hg .00

Cu 71.44-Zn 28.28-Hg .10 Cu 71.05-Zn 28.88-Hg .06 Cu 69.08Zn 30.9l-Hg .004 Cu 69.00-Zn 30.99-Hg .008 Cu 69.37-Zn 30.5l-Hg .04 GL1 70.21--Z11 29.78-Hg .00

Cu 84.70-Zn 15.29-Hg .008

Red Brass Cu 84.55-Zn 15.44Hg .00

Table 2 Alloy Weight 1 Tensile Pitting 8 Strength 2 Example A (Hg .04%) 0. 18 0. 25 7. 2 High Brass (Hg nil) 0. 53 0. 78 10. O(p.t.d)

Example B (Hg .07%) 0. 60 2. 60 0.0 Muntz Metal (Hg nil) 2. 70 i 8. 35 0.

Example 0 (Hg 05%)---" .32 .30 3.9 Admiralty (Hg n1l).--- 37 36 14. 0(p.t.d)

Example I) (Hg 26 .37 3. 8 Example E (Hg 06%).-- l6 28 7.9 Example F (Hg .004%) 26 .47 0. 8 Example G (Hg .008%) 28 13 0.8 Example H (Hg 04%).-- 23 23 5.3 70/30 Brass (Hg nil) 26 68 13. 5(p.t.d)

Example I (Hg 008%).-- 45 .49 7. 6 Red.- Brass (Hg nil) .44 .45 11.5

Norm-All values are the average of six or more tests.

1 Penetration in mils per year calculated from loss in weight.

Penetration in mils per year calculated from loss in tensile strength. I Depth of pitting or plug type dezincification (p.t.d) in five years.

Layer type dezincification.

In Table 3 below there is presented data regarding the ing examples versus related mercuryfree alloys. These values were determined after six months exposure to flowing Atlantic Ocean water flowing at a velocity of about two and a half feet per second.

Table 3 Rate of 11m plngement in Alloy mils per year Example A (Hg 04%) High Brass (Hg nil)...

Example B (Hg 07%).. Muntz Metal (Hg nil) Example 0 (Hg .05%) Admiralty (Hg nil) ExampleD Hg 10%).. Example E g .06%)

Example I (Hg 008%) Red Brass (Hg nil) brass is not substantially different, but the loss in tensile strength, which is due to dezincification, is markedly altered by the presence of mercury. This difference 1s brought out through the use of a ratio of rate of corrosion based on loss in tensile strength to the rate of cor When this ratio ape preaches unity (1.0) uniform corrosion tree from de-.

rosion based on loss in weight.

zincification is indicated. The data in Table 4 reveals that mercury in brass does act to a considerable degree as an eifective inhibitor of dezincification.

Table 4 Data showing improved resistance to dezincification by brasses containing mercury versus mercury-free brasses in 1% cupric chloride solution (78 day test):

Rate 0! Corrosion Loss in Alloy Based on Tensile Ratio,

Loss in Strength '1.S.lwt. Weight (T.S.)

Example A (Hg 04%)--- .0132 ipy. .0138 ipy. 1.0 High Brass (Hg nil)- .0158 ipy. .0644 ipy. 4.0 Example B (Hg .07 a .0131 .01805 1.4 Muntz Metal (Hg nil 1013 0. 6 Example 0 (Hg 05%) .0235 1.7 Admiralty (Hg nil)..." 06875 5. 3

Example D (Hg .10%) .01345 .01385 1.0 70/30 Brass (Hg nil) .0139 0072 4.0

rate of impingement corrosion for the mercury contain-. 75

Having thus set forth the nature of the invention, what is claimed is:

An anti-biofouling admiralty metal consisting essentially of approximately of copper, approximately 28% of zinc, approximately 1% of tin and mercury in an amount not in excess of 1% and not less than .001%.

References Cited in the file of patent UNITED STATES PATENTS 130,814 Macker Aug. 27, 1872 1,248,925 Sandell Dec. 4, 1917 2,270,660 Misfeldt Jan. 20, 1942 FOREIGN PATENTS 401,750 France Sept. 13.1909; 

1. AN ANATI-BIOFOULDING ADMIRALTY METAL CONSISTING ESSENTIALLY OF APPROXIMATELY 70% OF COPPER, APPROXIMATELY 28% OF ZINC, APPROXIMATELY 1% OF TIN AND MERCURY IN NA AMOUNT NOT IN EXCESS OF 1% AND NOT LESS THAN .001%. 